The present invention relates to a glass panel including at least three glass sheets for forming an air layer and a vacuum layer side by side and for partitioning between outdoor space and indoor space.
There is known a glass panel of the above-noted type which includes e.g. three glass sheets, with a vacuum layer being formed between the center glass sheet and one side glass sheet and an air layer being formed between the center glass sheet and the other side glass sheet, so as to provide a low thermal transmittance.
With the above-described conventional glass panel, the glass panel may achieve such low thermal transmittance and a high heat insulation because of the effects of the air layer and vacuum layer.
However, with this conventional glass panel, since the glass has high emittance, if such glass panel is employed in a window pane of an ordinary building, during winter season, the warm heat of the indoor space can be conducted in the form of infrared ray through the three glass sheets to be diffused to the outdoor space.
Here, the term: xe2x80x9cemittancexe2x80x9d is defined as the ratio of the heat re-radiated from the glass sheet relative to the total amount of heat irradiated on the glass sheet in case the heat is radiated from the glass sheet which was warmed by heat rays back to the outside.
The object of the present invention is to overcome the above-described drawback of the prior art by providing a glass panel having high heat insulation and capable of shielding heat rays such as infrared ray.
A multilayered glass panel, according to claim 1, is characterized in that at least either an outdoor-side glass sheet contacting the outdoor space or an indoor-side glass sheet contacting the indoor space of glass sheets G contacts the vacuum layer S and includes a low-emittance film layer M formed on a face thereof contacting the vacuum layer S.
If at least either an outdoor-side glass sheet contacting the outdoor space or an indoor-side glass sheet contacting the indoor space of glass sheets G contacts the vacuum layer S and includes a low-emittance film layer M formed on a face thereof contacting the vacuum layer S, as proposed by the present invention, this low-emittance film layer may reflect the infrared rays. So that, in addition to the heat insulating effects of the air layer and the vacuum layer, it is also possible to restrict heat diffusion from the indoor space which is being heated to the outdoor space. Therefore, the heat insulating effect may be further improved.
And, the glass panel of the present invention has the function of preventing heating of the glass sheets per se. That is, while the low-emittance film layer can effectively reflect far infrared radiation while the same layer can absorb near infrared radiation more readily than a glass sheet having no such low-emittance film layer. Therefore, when subjected to the sunbeam, the glass sheet with the low-emittance film layer is heated to a high temperature more easily than a glass sheet without such layer.
Suppose now the glass sheet with the low-emittance film layer comprises the center glass sheet of the glass panel. Then, once this glass sheet is heated due to the sunbeam, the heat will not be conducted to either space as both the space on the one side of the glass sheet and that on the other side of the same are heat-insulated, so that this glass sheet alone will be heated to high temperature. As a result, there will develop an excessive temperature difference between this glass sheet and the other glass sheet opposing thereto via the vacuum space, and consequently there may be developed a significant warp in the glass sheet which warp may even destroy this glass sheet.
On the other hand, in the case of the glass panel according to the present invention, the low-emittance film layer is provided on either the outdoor-side glass sheet contacting the outdoor space or the indoor-side glass sheet contacting the indoor space. Hence, when the temperature of the glass sheet with the low-emittance film layer begins to rise, the heat of this glass sheet may be readily diffused into the air of the outdoor space or the indoor space. Therefore, the above-described problem may be avoided.
Incidentally, according to the spirit of the present invention, it is only required that at least either one glass sheet, i.e. the outdoor-side glass sheet or the indoor-side glass sheet contact the vacuum layer and include the low-emittance film layer. That is, as long as either one glass sheet has the above feature of the invention, the construction of the other glass may vary as desired. For instance, it may be freely selected whether the other glass sheet too is provided with such low-emittance film layer or not, or whether this further low-emittance film layer if provided contacts the vacuum layer or the air layer.
According to a glass panel relating to claim 2, the low-emittance film layer M comprises a thin film containing, as the main component thereof, stannic oxide mixed with fluorine.
The above-described low-emittance film layer may be obtained for example by spraying an organic compound of tin, in the form of vapor, such as tin tetrachloride (SnCl4), dimethyl tin dichloride ((CH3)2SnCl2), or the like on to the surface of the glass sheet which is heated to e.g. 500 to 700xc2x0 C., with a carrier gas of e.g. nitrogen gas. In his, the thermal emittance may be further reduced if fluorine is added in the film.
With the above-illustrated method, there may be obtained a fluorine-containing stannic oxide film which has a thickness of e.g. about 0.2 to 1.0 xcexcm (2000-10000 angstrom) and which is transparent and electroconductive. In this case, the conductive electrons within the film provide the function of reflecting the infrared rays, so that the resultant glass panel obtains even superior heat insulating performance with the emittance ranging between 0.20 and 0.15 approximately.
Further, according to a glass panel relating to claim 3, the low-emittance film layer M comprises a thin film including at least one set of composite layer consisting of a silver layer and a pair of transparent dielectric layers opposed to each other across the silver layer.
If the low-emittance film layer is comprised of at least one set of composite layer consisting of a silver layer and a pair of transparent dielectric layers opposed to each other across the silver layer as described above, this thin film may effectively reflect the infrared rays in the sunbeam so as to further reduce the amount of infrared rays transmitted to the indoor space.
Silver has good electroconductivity so as to effectively reflect the infrared layers. However, with silver alone, its reflectance of visible light is high and also transparency required for a windowpane cannot be obtained. Therefore, if this silver layer is sandwiched between a pair of transparent dielectric layers of TiO2, ZnO, SnO2 or the like to restrict reflection of visible light, there may be obtained a multilayered film which is transparent and which yet reflects the infrared rays. The low-emittance film layer M obtained in the manner described above has a reflectance of about 0.10 to 0.05, thus achieving high heat insulating performance.
Further, by superposing more than two such composite layers, the reflectance of the low-emittance film layer M may be even reduced. For instance, if two sets of such composite layers are provided, the reflectance becomes 0.02 to 0.05. Then, there may be obtained a low-emittance film layer M having even superior heat insulating effect to the case where only one such composite layer is provided.
Incidentally, although reference marks are provided in the foregoing for facilitating reference to the accompanying drawings, it is understood that the provision of these marks is not to limit the construction of the present invention to those shown in these accompanying drawings.